Measurements over Canada’s Mackenzie River Basin suggest that thawing permafrost is starting to free greenhouse gases long trapped in oil and gas deposits.

Global warming may be unleashing new sources of heat-trapping methane from layers of oil and gas that have been buried deep beneath Arctic permafrost for millennia. As the Earth’s frozen crust thaws, some of that gas appears to be finding new paths to the surface through permafrost that’s starting to resemble Swiss cheese in some areas, scientists said.

In a study released yesterday, the scientists used aerial sampling of the atmosphere to locate methane sources from permafrost along a 10,000 square-kilometer swath of the Mackenzie River Delta in northwestern Canada, an area known to have oil and gas desposits.

Deeply thawed pockets of permafrost, the research suggests, are releasing 17% of all the methane measured in the region, even though the emissions hotspots only make up 1% of the surface area, the scientists found.

In parts of northern Canada’s Mackenzie River Delta, seen here by satellite, scientists are finding high levels of methane near deeply thawed pockets of permafrost.

In those areas, the peak concentrations of methane emissions were found to be 13 times higher than levels usually caused by bacterial decomposition—a well-known source of methane emissions from permafrost—which suggests the methane is likely also coming from geological sources, seeping up along faults and cracks in the permafrost, and from beneath lakes.

The findings suggest that global warming will “increase emissions of geologic methane that is currently still trapped under thick, continuous permafrost, as new emission pathways open due to thawing permafrost,” the authors wrote in the journal Scientific Reports. Along with triggering bacterial decomposition in permafrost soils, global warming can also trigger stronger emissions of methane from fossil gas, contributing to the carbon-climate feedback loop, they concluded.